Lean code to vac leaks and now... vacuum pump?

[spector]

Ok, so I finally found a shop that did a smoke test on my car and found that the underside of my TIP was all ripped to shreds, presumably causing my low vacuum at idle (~16-17mmHg). They replaced that and my vac at idle is now ~19mmHG. Also, they continued the smoke test after replacing the TIP and they found a leak in the vacuum pump over by the driver's side/radiator. From what I understand, the leak is in the casing of the pump itself, not the connecting hoses.

My question is, wtf is a vacuum pump and why isn't it on any of the vacuum system diagrams? He emphasized that it is NOT the suction jet pump, which is in good shape. Anybody have experience with this?

[spector]

Ok, it actually sounds like it's the brake booster pump that is leaking. Has anyone had experience with this part failing/leaking before?

P/N: 8E0 927 317 (NOT cheap... $300)

[Audi Skate Snow]

if you have a leak in your TIP it will not cause a vacuum leak... it will just get unmetered air in.

do you have a tiptronic?

[MikeWire]

Charlie's on it - must be a TIP if you have a secondary vac pump. Its got to be a check valve or something related to the suction jet pump.

[spector]

if you have a leak in your TIP it will not cause a vacuum leak... it will just get unmetered air in.

do you have a tiptronic?

Well, lean code is gone and idle vacuum has increased from -16-17mmHg to -19, so it looks like replacing the TIP was about 2psi worth of vac (edit: 2mmHG).

Yeah, I have a tiptronic.

Check valves are all somewhat new, as is the suction jet pump, and all check valves blow air in just one direction. Replacing the TIP is what improved my vacuum.

[Audi Skate Snow]

isnt there a vacuum pump gasket on those things? I have personally never had to deal with any when I worked at the dealer. but I believe there is a gasket on there that might leak.

[MikeWire]

Hey Charlie, it's a standalone pump - I have one on my car, and I deleted it with all my EGR and vac lines...it wasn't a good idea because I got two errors. One was related to the pump being unplugged (removed) and the other was referring to not enough vac on the brake booster. On the side of the pump you have one line (vac) and that's pretty much it. Down that line there is a check valve, and then that line goes up to the intake manifold and the suction jet pump IIRC to supply additional vac to the system.

Because I removed my EGR system I have hacked up my lines and made my own vac lines with check valves etc. so that everything works correctly. But if the problem lies with the pump, I am not sure how that would be possible, unless it has failed or there is a split line or check valve. It's also hard to diagnose because the lines need vacuum instead of pressure, so it's hard to do a smoke test or anything - the only thing you can try is a close visual inspection of all the lines, valves and clamps.

[spector]

isnt there a vacuum pump gasket on those things? I have personally never had to deal with any when I worked at the dealer. but I believe there is a gasket on there that might leak.

Hm, I can ask them to check. I certainly would prefer any course of action that saves me $300. Then again, I'm very paranoid about anything with the word "brake" in it.

[MikeWire]

Meh, I didn't notice a difference with it not hooked up, but I got a CEL with it unplugged. I just hooked it back up and ran the check valve and lines back because I want to delete vac lines, but still "do it right", whatever it's worth. My brakes work just fine, but you should still get it fixed. I doubt it's the pump and I'm still putting my $$ on a check valve or a vac line in the area.

Don't suppose you pulled any codes, and they didn't give you any codes or anything did they? Might be nice to get some insight if there are any codes.

Oh, and I should add that this only affects TIP cars, and on manuals there's just an empty space where the pump would sit. Great place for a meth pump.

[spector]

Meh, I didn't notice a difference with it not hooked up, but I got a CEL with it unplugged. I just hooked it back up and ran the check valve and lines back because I want to delete vac lines, but still "do it right", whatever it's worth. My brakes work just fine, but you should still get it fixed. I doubt it's the pump and I'm still putting my $$ on a check valve or a vac line in the area.

Don't suppose you pulled any codes, and they didn't give you any codes or anything did they? Might be nice to get some insight if there are any codes.

Oh, and I should add that this only affects TIP cars, and on manuals there's just an empty space where the pump would sit. Great place for a meth pump.

The pump isn't giving any codes, but he did say that there was a small (very small, apparently) amount of smoke coming out from an edge of the pump. I have recently replaced all but one of the original black check valves in the car (even those replaced the OEM two-tone ones) but I have verified that the single black check valve is in good shape and only blowing air in one direction.

I'm still intending to rip off the manifold and replace ALL those vac hoses in that area (or have the shop do it and save me the several hours of time + inevitably blowing something up) so I think I'll have them do that in a couple of months when I get some more cash.

Interestingly, after they replaced the TIP and vacuum improved a couple of mmHG, a run at WOT gave another CEL and the code was p0299. I immediately suspected the n75 (which was the original one in the car) and sure enough, the shop pulled the n75 and it was pretty boned. He replaced it with a reviison F, and my vac is now -19mmHg and the car is boosting to ~21psi. Kind of funny that the bad n75 didn't show itself until the vacuum improved. Oh, the joys of turbo cars...

[MikeWire]

Ah ok, well if I understand your description of what the shop did, if you push air/smoke down a line that is a vac line, the smoke is making it past the check valves because the air is going in the correct direction (towards the pump), and the pump shows smoke because the vac pump has to output the air - maybe I am misunderstanding, but that sounds normal to me.

From what you are saying it sounds like all is good, but you obviously still have a small vac leak somewhere. Check all those one-time clamps on the vac lines - they loosen up over time, and/or replace them all with worm style clamps.

An old skool DIY trick to look for vac leaks is to *lightly* spray a little carb cleaner on the vac lines and joints, and if the idle picks up you have a leak on that spot. Of course that would only work on lines that run to the manifold and the car would need to be at idle (so there is vacuum).

I would think that if the pump has failed you would get a code. Mine runs after start up, so if you wanted to test it, pull the hose off the pump and start the car - you should hear it fairly well with that hose off.

[spector]

Thanks, those are useful comments. I'll try the carb cleaner suggestion down by the intake hoses.

Fortunately, most of the one-time hose clamps have been removed as I've replaced vac components. All that's left is the original shizzle under the manifold. It does sound like the smoke made it all the way through those vac components and into the pump, so maybe that means those hoses and lines are holding up OK for now? I fully intend to replace them by the end of the year, but they only need to last a couple more thousand miles...

FYI, my car is up in north Atlanta right now, which is at ~1000ft elevation, so I'd expect vac to be *slightly* lower than when I am home in Florida, perhaps by a single mm of HG or so. I think the dudes in Colorado have normal idle vacuum at like 15mmHg, and you probably have some of the same in Montana. I don't know how much it varies though. Either way,I'll take -19 at idle over -16 or -17. Hell, the car would be at -9 to -11mmHg when I was in gear sometimes.

[MikeWire]

Cool glad to help another TIP owner, as things are a little different with that extra vac pump. I'm not sure what to expect being at your elevation, but I am at about 3300ft above sea level. I haven't driven my car in a while, but I know I get about -20hg at idle, especially now that I have "simplified" my vac system. Sounds like you know whats up, so good luck and update us on your progress!

[spector]

isnt there a vacuum pump gasket on those things? I have personally never had to deal with any when I worked at the dealer. but I believe there is a gasket on there that might leak.

Ding ding ding!

Thanks, man, this looks like the culprit. I have to return a part to the stealership this weekend, I'm going to see if they have the gasket. If not, the shop said they can rig me one up before we try replacing the part.

Btw, got my car back today after they replaced the ruptured TIP and the original n75 and HOLY SHIT it's like driving a new car. I wonder how long that stuff was broken.. probably since I've been modding my car. I don't think I've ever got to take full advantage of any of my performance mods until now. Completely night and day. I am a very happy driver.

[Audi Skate Snow]

nice... glad we can help out. P.S that gasket is super cheap and the dealer should have it on hand. Good to see it is getting worked out.

[spector]

nice... glad we can help out. P.S that gasket is super cheap and the dealer should have it on hand. Good to see it is getting worked out.

Well, I went to the dealer and he says that he can only sell the whole thing as a unit... has no idea about the gasket. This is the part in question:



And here is a close up:


It looks like that part number is 8E0 927 317. I can only find a few sources for that online and don't have any idea where to find the gasket. My shop says they can fab one up for me if I want, but would anyone know where I can locate the gasket for that thing? I'd really hate to have to spend $300 on the whole pump. Any suggestions?

[diagnosticator]

It is normal for some test smoke to come out of the brake booster vacuum pump during the leak test. (The hose connected to the vac pump should be disconnected and plugged for the test.)

The reason is because the vacuum system is at a higher pressure than the surrounding ambient air pressure during the leak test, and the flow direction is normally from the brake booster to the outside air via the vacuum pump.
The vac pump uses two checks, one allows air into the pump, but blocks reverse flow back out of the inlet port, this is the port connected to the brake booster. The other check valve allows pumped air out of the pump via the exhaust port to atmosphere, and blocks atmospheric air pressure from flowing into the pump and the brake booster via the pump exhaust port if the inlet check is not sealing tight, as a backup.

There is a booster housing vacuum pressure sensor on the brake booster that sends a booster vacuum pressure level signal to the ECU. When certain operating conditions conspire to limit engine intake manifold vacuum available to the brake booster. As the brakes are applied booster vacuum pressure (absolute pressure,) increases. The ECU runs the vacuum pump to reduce the booster vacuum pressure to insure that the ABS and foot brake pedal braking power are sufficient to stop the car safely regardless of the occasionally limited vacuum pressure available from the engine.

BTW, the brake booster housing vacuum pressure can be observed using VCDS in the Engine ECU measuring blocks. Units are millibar absolute pressure. Also, note that the units for vacuum pressure shown on your boost pressure gage, is "inches HG". (HG=Mercury) Compared to "mmHG' the relevant pressure range is on a different range scale. (1 inchHG= 25.399 mmHG = 33.86 millibar).

[spector]

It is normal for some test smoke to come out of the brake booster vacuum pump during the leak test, the reason is because the vacuum system is at a higher pressure than the surrounding ambient air pressure during the leak test, and the flow direction is normally from the brake booster to the outside air.

The vac pump uses two checks, one allows air into the pump, but blocks reverse flow back out of the inlet port, this is the port connected to the brake booster. The other check valve allows pumped air out of the pump via the exhaust port to atmosphere, and blocks atmospheric air pressure from flowing into the pump and the brake booster via the pump exhaust port if the inlet check is not sealing tight, as a backup.

There is a booster housing vacuum pressure sensor on the brake booster that sends a booster vacuum pressure level signal to the ECU. When certain operating conditions conspire to limit engine intake manifold vacuum available to the brake booster, as the brakes are applied booster vacuum pressure (absolute pressure,) increases. The ECU runs the vacuum pump to reduce the booster vacuum pressure to insure that the ABS and foot brake pedal braking power are sufficient to stop the car safely regardless of the occasionally limited vacuum pressure available from the engine.

BTW, the brake booster housing vacuum pressure can be observed using VCDS in the Engine ECU measuring blocks. Units are millibar absolute pressure.

Ok, so that explains my mechanic's concerns that any air leaking meant that the system wasn't holding vacuum and why smoke coming out isn't necessarily a problem.

It sounds like if there were something wrong I'd have codes and/or possibly brake trouble?

Thanks, as always, for the explanation, even though I had to read it 5 times. ;-)

[diagnosticator]

Ok, so that explains my mechanic's concerns that any air leaking meant that the system wasn't holding vacuum and why smoke coming out isn't necessarily a problem.

It sounds like if there were something wrong I'd have codes and/or possibly brake trouble?

Thanks, as always, for the explanation, even though I had to read it 5 times. ;-)

Sorry, I was trying to be brief and clear. FWIW, I had to edit about 15 times:-|

I agree, if there was an electrical or mechanical fault with the vac pump, there would be one or several DTCs stored, either "booster housing pressure to high" or similar or "vac pump circuit open/shorted', etc.

And as you expect, there could be one or several brake/ABS operational problems as well.

[MikeWire]

No offense to you diagnosticator, but I pretty much already told Spector what you posted, although I didn't get as technical about it as you did. I liked reading your paragraphs anyhow - always informative as usual.

Spec, after your last post, I think that the tip and your N75 were your problem, and your sec. vac pump is fine...after all it is a very simple part, and only does one task. If you have no codes related to the pump or your brake booster, then all is well and glad your problem has been resolved.

[spector]

Yes, MikeWire, and thanks for the comments. When I first told the mechanic what you told me he was like "I think the whole system should be able to hold vac..." but between what both of you have written it makes sense now. At any rate, car is pulling strong, lean code is gone, and even my gf notices a significant increase in torque. I'll still be swapping the vac system under the manifold soon, but it's holding great right now.